The present invention generally relates to switches used in conjunction with antennas and, more particularly, to a MEMS transfer switch for use in coupling a radio frequency (RF) signal to an antenna or an RF signal received by an antenna to an associated circuit.
A wide variety of antennas are used to transmit and/or receive signals at microwave or millimeterwave frequencies. These signals (commonly referred to as radio frequency (RF) signals) often pass through switches between a transceiver circuit and the antenna. In some applications, a transfer switch is used to simultaneously route two input signals among two outputs of the switch (e.g., a double pole, double throw switch).
As an example, U.S. Pat. No. 5,874,915, the disclosure of which is herein incorporated by reference in its entirety, discloses a wideband electronically scanned cylindrical UHF antenna array and associated beamforming network that uses a matrix of electronically controlled transfer switches. The electronically scanned array (ESA) disclosed in the ""915 patent can be used, for example, as part of an airborne early warning (AEW) radar. In the past, such transfer switches have been implemented with PIN diodes, gallium arsenide (GaAs) field effect transistors (FETs), latching circulators and electromechanical devices such as relays.
Conventional transfer switches formed with PIN diodes, FETs, latching circulators and relays have been known to introduce undesirable amounts of insertion loss, especially for relative high RF bands. In addition, latching circulators have a relatively narrow bandwidth, slow switching speeds, and require a current driver. Latching circulators tend also to be large and heavy making their use in some airborne applications impractical. Furthermore, relays have a relatively slow switching speed that can be too slow for scanning applications.
Another drawback of conventional transfer switches is that splits or xe2x80x9cteesxe2x80x9d in the input and output transmission lines are used to connect the transmission lines to the switches. When a switch is placed in an open position, the tee acts as a capacitive stub that can result in an impedance mismatch in the signal path. As a result, the tee limits the bandwidth of the device.
Accordingly, there exists a need in the art for higher performance transfer switches for use in RF applications.
According to one aspect of the invention, the invention is directed to a micro electro-mechanical system (MEMS) transfer switch. The MEMS transfer switch includes a first and a second radio frequency (RF) input transmission line; a first and a second RF output transmission line; and a plurality of series MEMS switching units operatively arranged with the input and output transmission lines to selectively connect either the first input transmission line to the first output transmission line and the second input transmission line to the second output transmission line or the second input transmission line to the first output transmission line and the first input transmission line to the second output transmission line.
According to another aspect of the invention, the invention is directed to a micro electro-mechanical system (MEMS) transfer switch for simultaneously connecting two radio frequency (RF) input transmission lines among two RF output transmission lines. The MEMS transfer switch includes a first MEMS switching unit positioned to electrically couple a contact engagement end of a first of the input transmission lines and a contact engagement end a first of the output transmission lines when the first switching unit is placed in a closed position; a second MEMS switching unit positioned to electrically couple a contact engagement end of a second of the input transmission lines and a contact engagement end a second of the output transmission lines when the second switching unit is placed in a closed position; a third MEMS switching unit positioned to electrically couple the contact engagement end of the first of the input transmission lines and the contact engagement end the second of the output transmission lines when the third switching unit is placed in a closed position; and a forth MEMS switching unit positioned to electrically couple the contact engagement end of the second of the input transmission lines and the contact engagement end the first of the output transmission lines when the fourth switching unit is placed in a closed position.